Fracturing of well formations is a very difficult art. According to the known procedures, the formation area which may be fractured by a fracturing treatment is limited. In order that the area of fracture may be increased, the fracturing fluid used must have a viscosity low enough to permit adequate penetration through the particular formation and at the same time high enough to prevent coefficient that excessive leak-off of fracturing fluid to the formation not occur. Fracturing fluids in the past have of necessity been formulated based on compromise between low viscosity for high formation penetration and high viscosity to prevent excessive leak-off of fracturing fluid. At the same time, the fluid must be capable of delivering the sand or other particulate matter into all parts of the fracture area. In other words, the sand should not fall from suspension in the fracturing fluid or the benefits of fracturing will not be fully realized.
In addition to the requirements of high formation penetration, low fluid loss, and satisfactory sand carrying ability of the fracturing fluid for a successful well fracturing operation, other factors are important. Well formations often contain materials which are sensitive to various liquids. In particular, the swelling clays are notably affected by water. Therefore, the amount of water used in fracturing these formations should be kept at a minimum. When a large amount of fracturing fluid (liquid) is employed in well fracturing operations, problems can occur in removing a sufficient amount of water from the formation following the fracturing treatment in order to secure adequate production from the well.
According to many well fracturing procedures, control of the fracturing operation is difficult. Not only are the factors mentioned above important, but adequate control of the fracturing fluid flow into the formation, and flow back out of the formation following completion of fracturing, is also important. The propping material must also be left in proper disposition in the formation to adequately increase production flow from the formation. The fracturing fluids afforded by this invention provide these controls, and in particular the invention affords full control of bleedback to the well of the fracturing fluid after fracturing is completed.